yet he has a super patronus?
Heres my theory on the Patronus charm.
A Happy memory is not, exactly, what is required for the spell.
It is the contrast between the persons typical memories and the chosen one, that powers the spell. A, sign if you will, of how special that memory is.
For Harry, that is a huge contrast with the memory of Sirius asking him to live with him. The not-happy-whatsoeverness of living with the dursleys, and the prospect of living with a godfather who would treat you right (once he got sorted out and not all stick-man-from-azkaban.)
On the other hand, most people can't cast a patronus, yet surely they have happy memories with their families?
Oh hold on, they don't have the numerous darker memories to bring down the average to a point that the contrast is even anywhere near what it is with Harry.
What do you all think?
Sink or help this theory swim as you want.